1. Field of the Invention
The present invention relates to an information processing apparatus for moving a recording medium mounted on a carriage with respect to a head to record information on the medium and/or reproduce the information from the medium.
2. Description of the Related Art
Disk, card-like, and tape-like information recording media are known as conventional information recording media. Some information recording media can record and reproduce information, and some can only reproduce information. In a recordable information recording medium, information tracks are scanned with a light beam spot having a small diameter and modulated in accordance with given recording information to record the information as an optically detectable information bit array.
In order to reproduce information of a recording medium, a given information track is scanned with a light beam having a power low enough not to record information on the recording medium, and a beam reflected by the surface of the medium or transmitted through the medium is detected. Therefore, information can be read from an information bit array of an information track.
In an optical information processing apparatus for recording or reproducing information on or from an information recording medium, a so-called "optical head" must be used to irradiate the recording medium with a light beam spot and detect a beam reflected by or transmitted through the medium. The optical head is movable in an information tracking direction and a direction perpendicular to the information tracking direction with respect to the recording medium. A relative displacement allows scanning of the information track with a light beam spot. In the optical head, part of the optical system, e.g., an objective lens is held to be movable independently in a direction along its optical axis (focusing direction) and a direction (tracking direction) perpendicular to the optical axis and in the information tracking direction of the recording medium. The objective lens is generally held through an elastic member. Movement of the objective lens in the above focusing and tracking directions is generally performed by an actuator utilizing an electromagnetic interaction.
Recording and reproduction of a card-like optical information recording medium (optical card) shown in FIG. 1 will be described below.
Referring to FIG. 1, a large number of parallel information tracks 2 extend on an information recording surface of an optical card 1 in the D.sub.1 -D.sub.2 direction. A home position 3 is defined on the information recording surface and serves as a reference position for access of the information tracks 2. The information tracks 2 are arranged in an order of 2-1, 2-2, 2-3, . . . from the side near the home position 3. Tracking tracks (e.g., 4-1, 4-2, 4-3, . . . ) are formed adjacent to the information tracks 2 (e.g., 2-1, 2-2, 2-3, . . . ) on the information recording surface. The tracking tracks are utilized as a guide for auto-tracking (AT) a light beam spot in the recording and reproduction modes so as to accurately trace a predetermined information track with the light beam spot. In an optical information recording/reproducing apparatus, AT servo control is performed for AT. According to AT servo control, when a deviation of the light beam spot from the information track is detected (i.e., an AT error), a detection signal is negatively fed back to the tracking actuator to move the objective lens relative to the optical head so as to adjust the position of the objective lens in the tracking direction. Therefore, the light beam spot can trace the information tracks.
When the information tracks are scanned with the light beam spot in the information recording/reproduction mode, the light beam must be focused to form a spot having an optimal size (i.e., the light beam must be set in an in-focus state) on the information recording surface of the optical card. For this purpose, auto focusing (AF) servo is performed in the optical information recording/reproducing apparatus. In AF servo control, a deviation of the light beam spot from an in-focus state (i.e., an AF error) is detected, and the detection signal is negatively fed back to the focusing actuator, thereby moving the objective lens with respect to the optical head such that the objective lens is aligned with the focusing direction. Therefore, the light beam spot can be set in an in-focus state on the surface of the optical card.
Light beam spots S.sub.1 and S.sub.3 in FIG. 2 are used for tracking, and light beam spot S.sub.2 is used for performing focusing control, forming an information pit in the recording mode, and detecting the information pit in the reproduction mode. Address portions 6-1, 6-2, 6-3, . . . are preformatted on the information tracks 2-1, 2-2, 2-3, . . . to discriminate the respective information tracks. Data portions 5-1, 5-2, 5-3, . . . follow the address portions 6-1, 6-2, 6-3, . . . . When an information track is scanned with the light beam spot S.sub.2, a track number is read out from the address portion, and information is recorded in the data portion or read out therefrom to perform reproduction.
When the optical card having the above arrangement is used in an optical information processing apparatus, the following card feeding mechanism must be used. The card feeding mechanism has an arrangement shown in FIG. 3. The optical card 1 is fixed on a carriage 44 through card holders 8. Each of the card holders 8 has a groove-like shape. When the optical card 1 is slid along the upper surface of the carriage 44 from the backward direction, and abuts against a card abutment plate 7, the card holders 8 hold the optical card 1. The carriage 44 has slide bearings 46 on both its sides, and parallel slide shafts 47 extend through the corresponding slide bearings, so that the carriage 44 can be moved along the slide shafts 47 in a direction D.sub.1 (or a direction D.sub.2 opposite to the direction D.sub.1). A coil core is arranged below the carriage 44. A coil 43 is wound around the coil core. Yokes 48 and 49 fixed on the main body of the apparatus extend above and below the coil 43 along the moving direction of the carriage 44. The yokes 48 and 49 are coupled together with a yoke 51 extending through the center of the core of the coil 43, and both ends of the yokes 48, 49, and 51 are connected to iron pieces 52, thereby constituting a magnetic circuit. For this reason, permanent magnets 53 and 54 are arranged in the yokes 48 and 49 such that their N poles oppose each other and S poles oppose each other. With this arrangement, when current flows through the coil 43, a drive force for driving the carriage 44 in the direction D.sub.1 or D.sub.2 is obtained in accordance with the direction of the current.
A linear encoder 31 is arranged on one side of the carriage 44. The linear encoder comprises a belt having parallel slits extending in the direction D.sub.1 /D.sub.2 and a pulse detector such as a photodiode moved together with the carriage 44 to count the slits of the belt. Therefore, a displacement of the optical card upon movement of the carriage 44 can be indirectly detected.
A light-shielding plate 35 is also disposed on one side of the carriage 44 to extend parallel to the direction D.sub.1 /D.sub.2. A position sensor 32 (left sensor 33 and right sensor 34 each consisting of a light-emitting element and a light-receiving element) for detecting the position of the carriage 44 upon shielding of light by the light-shielding plate 35 is fixed on the apparatus main body. These sensors are so-called photointerrupters. The mounting position of the position sensor 32 is set such that the light-shielding plate 35 shields light incident on the left sensor 33 when the carriage 44 is accelerated from the right end in the direction D.sub.1 and reaches a constant speed, and that the shielding plate 35 shields light incident on the right sensor 34 when the carriage 44 is accelerated from the left end in the direction D.sub.2 and reaches a constant speed. The sensors 33 and 34 of the position sensor 32 are set at high level when light is not shielded by the light-shielding plate 35. However, when light is shielded by the light-shielding plate 35, the sensors 33 and 34 are set at low level.
In the optical information processing apparatus having the card feeding mechanism described above, after the optical card 1 is loaded on the carriage 44, the carriage 44 is accelerated in the direction D.sub.1 from the right end. When the carriage 44 reaches a constant speed, addressing is performed from a time when the left sensor 33 goes low to a time when the right sensor 34 goes high. Data write/read access is performed. When the right sensor 34 goes high, a predetermined number of pulses are counted by the linear encoder 31. When the count of the linear encoder 31 reaches the predetermined number, a reverse command is output to reverse the drive direction of the carriage 44 (i.e., the direction of the current supplied to the coil 43 is reversed). After the reverse operation, the carriage 44 is accelerated in a direction D.sub.2. When the right sensor 34 goes low and then the left sensor 33 goes high after the carriage 44 reaches a constant speed, a predetermined number of pulses are counted by the linear encoder 31. When the count of the linear encoder 31 reaches the predetermined number, a reverse command is output to reverse the drive direction of the carriage 44.
The reverse operation, addressing, data write/read access are performed with reference to the carriage position in the optical information processing apparatus described above. Unless the optical card 1 is accurately loaded, operation errors such as an addressing timing error occur. In order to solve this problem, a card position detector 9 shown in FIG. 3 is arranged in the conventional optical information processing apparatus. A reflection photoswitch is often used as the card position detector 9. When the optical card 1 abuts against the card abutment plate 7 and is accurately loaded on the carriage 44 while the carriage 44 is located at a given position, light reflected by an end of the optical card 1 returns to the card position detector 9. For this reason, when the optical card 1 is loaded in front of the card abutment plate 7, no light reflection from the end of the optical card 1 is detected. Therefore, an inaccurate card position is discriminated.
An apparatus for detecting a loading state of a card by using an optical head in place of the above card position detector is described in Japanese Patent Laid-Open (Kokai) No. 61-280073.
In either conventional apparatus, the card loading state is detected. When the card loading position on the carriage is inaccurate, re-loading is time-consuming. If the carriage 44 is fed without re-loading the optical card 1, recording/reproduction is performed on the information tracks in a region where the moving speed of the carriage is unstable. Thus, accurate recording/reproduction cannot be performed.